Hard-disk drives (HDDs) have been widely used as data-storage devices that have proven to be indispensable for contemporary computer systems. Moreover, HDDs have found widespread application to moving image recording and reproducing apparatuses, car navigation systems, cellular phones, and similar devices, in addition to the computers, due to their outstanding information-storage characteristics.
As information-storage technology advances and the range of applications for the use of HDDs has increased, the demand for HDDs with larger capacity, higher recording density and higher speed access has grown. In order to meet this market demand, high track-density and high bit-density magnetic-recording disks have come into use in HDDs. Furthermore, HDDs that rotate magnetic-recording disks, and move actuators to access data, at high speeds have been developed to meet these demands. For HDDs with higher recording density and higher speed access, improvement in the accuracy of positioning head-sliders to access data is highly desirable.
However, at such high speeds, the accuracy of positioning head-sliders is affected by “flutter” of the magnetic-recording disk, a term of art for a form of vibration affecting the magnetic-recording disk. Flutter affects magnetic-recording disks, when rotated by a spindle motor, through vibration in the axial direction of the spindle upon which magnetic-recording disks are mounted. Flutter of magnetic-recording disks mainly depends on the accuracy of assembly of magnetic-recording disks within the HDD and airflow caused by the rotation of the magnetic-recording disks. Reducing the flutter of magnetic-recording disks is one way to improve the accuracy of positioning head-sliders. Thus, engineers and scientists engaged in the development of new HDD technology are interested in means for increasing the mechanical stability of magnetic-recording disks and suppressing vibration, for example, due to flutter, in HDDs.